Hydraulic systems typically convert power between mechanical and hydraulic forms. Common types of hydraulic systems include hydraulic pumps, hydraulic motors, hydraulic cylinders, control valves, hydraulic accumulators and other components.
Some advantages of utilizing hydraulic systems include power density, continuously variable power transmission, a stiff dynamic response, flexible connections, and more. Although hydraulic systems exemplify many advantages over other power transmitting and control devices, these systems are also known for several drawbacks. Some drawbacks include a requirement for fine tolerances in the design and manufacture, utilizing the hydraulic fluid as lubrication under intense temperature conditions, and finally system efficiency.
FIG. 1 illustrates an example prior art axial-piston pump 10. The axial-piston pump 10 includes a drive shaft 11 coupled to a piston block 17 by a splined connection such that the drive shaft 11 and the piston block 17 rotate as a unit about a central longitudinal axis 9 of the drive shaft 11. The piston block 17 defines a plurality of cylinders 16 that receive pistons 12. The pistons 12 include elongated body portions 15 that reciprocate linearly within the cylinders 16. The elongated shape of the body portions 15 facilitates the transfer of torque between the piston block 17 and the pistons 12. The pistons 12 also include heads 19 secured within hydrostatic shoes 18 mounted within pockets defined by a carrier plate 14. The hydrostatic shoes 18 bear against a swash plate 13 that can be pivoted relative to the drive shaft 11 to vary the stroke length and thus the volumetric displacement of the axial-piston pump 10 at a given rotational speed of the drive shaft 11. In operation, torque from the drive shaft 11 is transferred through the piston block 17 and the pistons 12 to the hydrostatic shoes 18 thereby causing them to rotate relative to the swash plate 13 about the central longitudinal axis 9. As this group of components rotates, torque is resolved into axial pumping forces on the pistons 12 due to a non-zero swashplate angle. The transfer of pumping torque from the piston block 17 through the pistons 12 and the hydrostatic shoes 18 causes side load to be applied to the pistons 12 at the interface between the pistons 12 and the hydrostatic shoes 18. This side loading can cause the elongated body portions 15 of the pistons 12 to skew within their corresponding cylinders 16 thereby producing drag that can reduce the operating efficiency of the axial-piston pump 10. Improvements in this area would be beneficial.